To remove solid particulates containing carbon as a main component from a combustion exhaust gas exhausted, for example, from a diesel engine, a filter for purifying an exhaust gas (hereinafter referred to simply as the “filter”) has heretofore been used in which one-end portions of predetermined through-holes of a honeycomb structure formed of a porous ceramic material and including a large number of through-holes are plugged, the other end portions of the remaining through-holes are plugged, and partition walls partitioning the through-holes are formed as filter layers.
FIG. 6 is a schematic diagram showing a plugged state of a filter end surface. Plugged portions 10 constituted by charging a plugging material into end portions on opposite sides in adjacent through-holes (cells) 3 (shown in FIG. 5) are alternately formed to close the through-holes (cells) 3 in such a manner that the end surface of the filter has a checkered pattern in the shown state. FIG. 5 is a schematic diagram showing a plugging structure of a conventional filter for purifying the exhaust gas. The plugged portions 10 are formed in the one-end portions of the through-holes (cells) 3 and the other end portions of the remaining through-holes (cells) 3, and accordingly partition walls 2 partitioning the through-holes (cells) 3 bear functions of filter layers.
In recent years, resulting from technical progress of the diesel engine, especially high pressure injection of fuel, miniaturization of solid particles exhausted from the diesel engine has advanced, and there has been an increasing expectation for development of a diesel particulate filter (DPF) for use in capturing such fine solid particulates.
Moreover, there has been a growing interest in an environmental problem, restrictions on the exhaust gas have also became tighter, and a filter which is capable of more effectively capturing the solid particulates and which has characteristics such as high porosity and thin wall has been developed at fever pitch.
Although the increasing of the porosity of the partition wall and the thinning of the wall are realized, there is a tendency that strength of the partition wall decreases, and therefore a problem easily occurs that defects such as chipping and cracking are easily caused also by a slight impact load. Therefore, careful attentions need to be paid during not only packing and transporting of products but also canning process and handling of the products.
Especially, boundaries between the plugged portions 10 into which the plugging material is charged and the through-holes (cells) 3 into which the plugging material is not charged in FIG. 5 are sometimes cracked, and accordingly the defects such as chipping and falling-off of the plugged portions are generated in many cases. This is supposed to be a phenomenon resulting from a difference in strength between the plugged portions 10 and the through-holes (cells) 3, but this problem has become tangible with the increasing of the porosity of the partition wall 2 and the thinning of the wall, and there has been a demand for a concrete countermeasure.
The present invention has been developed in consideration of the problems of the related arts, and an object thereof is to provide an exhaust gas purifying filter which has characteristics such as high porosity and thin wall but which hardly causes defects such as chipping and falling-off of plugged portions during packing, transporting, or handling.